Keep vanetza-idf in obu-firmware, so a plain clone builds the firmware

obu-firmware builds against the vanetza-idf C-ITS library, which until now
came from the colleague's microbu-esp32c5 tree beside the repository and was
not tracked here, so a clone of this repository could not build the firmware
it ships. The library alone is now part of obu-firmware, as
obu-firmware/external/vanetza-idf: their external/vanetza-idf at commit
cf4b99f, unchanged (9775 files; see its PROVENANCE.md). CMake takes it from
there by default; -DVANETZA_IDF_DIR still points the build elsewhere.

The rest of the colleague's tree (their own VAM firmware, PKI tooling,
station-link Python tools, the V2X2MAP bridge) stays out of this repository
and gitignored; nothing is pushed to their repository. NOTES.md, docs/06,
TODO.md and the pcap verifier's usage line point at the new location.

obu-firmware/external/vanetza-idf/vanetza/common/clock.hpp

@@ -0,0 +1,40 @@
+#ifndef CLOCK_HPP_2FCBLXSJ
+#define CLOCK_HPP_2FCBLXSJ
+
+#include <boost/date_time/posix_time/posix_time_types.hpp>
+#include <chrono>
+#include <cstdint>
+#include <ratio>
+
+namespace vanetza
+{
+
+/**
+ * A Clock similar to std::chrono with epoch at 2004-01-01 at midnight
+ */
+class Clock
+{
+public:
+    typedef int64_t rep;
+    typedef std::ratio<1, 1000 * 1000> period;
+    typedef std::chrono::duration<rep, period> duration;
+    typedef std::chrono::time_point<Clock> time_point;
+    typedef boost::posix_time::ptime date_time;
+
+    static constexpr bool is_steady() { return true; }
+    static time_point at(const date_time&);
+    static date_time at(const time_point&);
+    static const date_time& epoch();
+
+    /**
+     * \brief create time point
+     * \param at time string formatted like 2016-07-15 09:48:32
+     * \return time point
+     */
+    static time_point at(const std::string& at);
+};
+
+} // namespace vanetza
+
+#endif /* CLOCK_HPP_2FCBLXSJ */
+